I know this is an old version and it will never be fix, but this may help anyone searching a reason why his icons are not showing.
I'm working in FMA16 but the rest in my office still use FM14 and I in the process of updating the design and functions.
I design a new style for the calendar and dropdown field, as I was using an old file updated from FM11, I never customized the icon on those field, now I'm doing it and discover that the icon go missing if the field right border is not selected, but only in FM14, not 16. Maybe it's already been submitted ? but I have found anything, as I was searching why my icon was MIA !! So if this could help someone some day, you now know why !
and the final result on FM14